Throughout the world, increased emphasis is being placed on proper initial well completion as the value of non-renewable oil reserves increases and cost of remedial work sky rockets. Maximum reliability and productivity are particularly essential offshore and in remote locations. These objectives are difficult to obtain where formation sands are unconsolidated or otherwise subject to failure. Sand control problems are most common in younger, tertiary sediments. However, sand inflow can occur in other formations if existing insitu stresses are altered by drilling and/or completion operations such that the rock matrix is weakened by movement of the borehole wall.
Sand flow from unconsolidated formations is controlled through chemical or mechanical means to prevent or correct various problems, the most common of which is premature failure of artificial lift equipment. Other potentially serious and costly problems include production loss caused by sand bridging in casing, tubing and/or flow lines; failure of casing or liners from removal of surrounding formation, compaction, and erosion; abrasion of downhole and surface equipment; and handling and disposal of produced formation materials.
Experience indicates sand control should be installed before the reservoir rock is seriously disturbed by sand removal. And it becomes more difficult to control further sand flow as the volume of produced sand increases. Thus, it is not surprising that initial sand control installations prove to be far more successful than remedial treatments. It is also fairly common for remedial installations, for a number of reasons, some of which are not fully understood, to impair productivity.
Sand control methods may be classified as mechanical bridging installations such as gravel-packs, slotted liners or prepacks, consolidated gravel, etc. or consolidation by injection of chemicals into the formation to provide insitu, grain to grain cementation. The simplest, most consistently reliable approach to sand control is application of mechanical sand retention devices. Screens, slotted liners, prepacked liners, and gravel are being used. An important design consideration is the proper sizing of liner openings or gravel pore space relative to the size of producing formation particles.
Gravel-packs are widely applied in wells that are cased and perforated through multiple and/or thin productive sections, or where it is necessary to exclude interbedded water, gas, or undesirable shale streaks. Important advances in the application of gravel-packs has significantly reduced failure frequency and improved productivity of the inside casing gravel-pack. These major advances are the results of improved perforation clean up practices, better use of completion fluids, and application of smaller gravel sizes.
For gravel-pack it is necessary to squeeze fluids into the formation during gravel placement to fill perforation tunnels with compacted gravel. Other perforations will be non-productive if their tunnels fill to some degree with formation sand during production. In a two-stage gravel-pack, the first stage involves the application of squeeze pressures to force gravel into and outside the perforation tunnel. The second stage normally consists of circulating gravel into place in the screen casing annulus, allowing gravel to be strained from excess carrier fluid as the fluid passes through the screen and returns to the surface.
The two most common techniques for controlling sand production are gravel-packing and sand consolidation. Sand consolidation is a technique wherein after perforating, some type of a liquid consolidation resin is pumped into the perforations to make each sand grain bond to other sand grains with which it is in contact. This leaves a consolidated sandstone formation which will not produce sand. The consolidation treatment to be effective must not greatly reduce the permeability of the previously unconsolidated formation. Also, to be effective every perforation must accept the consolidation resin and consolidate the sand around the perforation tunnel. If even one perforation does not accept resin then that perforation causes the well to produce sand and the treatment will have to be performed again. Normally, after perforating underbalanced, some type of a heavy fluid is placed in the well to prevent the well from flowing. When this is done the fluid damages the sand near the perforations. If the damage is severe, then no fluid will enter the damaged perforations. Afterwards, when the consolidation treatment is performed, some of the perforations will take fluid and others will not, which leads to an unsuccessful consolidation treatment.
In a gravel-packing operation, after the well is perforated, a screen is placed inside of the well that is across from all of the perforations. This screen has a diameter which is smaller than the inside diameter of the casing. Gravel is placed between the perforations and the screen. The gravel is of such a diameter that the formation sand will not be able to flow through it. The gravel placed in the well bore is of such a size that it will not be able to flow through the screen. This prevents sand production, yet oil or gas can still be produced through the gravel and the screen.
Conventional perforating techniques require that the well be perforated and then killed with heavy clean, clear brines while the perforating guns are removed from the hole. This process takes time and the brine normally reduces the productivity of the well because it damages the permeability of the formation. Present techniques exist whereby perforating and gravel pack can be accomplished in a single well trip. Such conventional single trip perforating/gravel-packing methods run standard gravel pack equipment and tubing conveyed perforating guns at the same time on the same work string. The tubing conveyed perforating gun is attached below the gravel-pack equipment. The conventional system is operated as follows: (1) The assembly is lowered into place so that the tubing conveyed perforating guns(s) are located across the zone to be perforated, (2) a firing head is activated by one of several triggering methods, (3) the firing head causes the perforating gun to fire, perforating the formation (4) formation fluids flow into the wellbore, if the formation has been perforated in an underbalanced pressure condition,(5) the perforating gun is disconnected from the gravel-pack equipment and drops to the bottom of the wellbore (6) the gravel-pack equipment is placed across the perforated zone by: (a) killing the well with an appropriately weighted completion fluid to isolate the rig floor from the reservoir pressure and lowering the gravel-pack equipment into position, or by (b) lowering the gravel-pack equipment into position using time consuming snubbing procedures and controlling reservoir pressure on the rig floor (7) Conventional gravel-pack procedures are then implemented.
While imperative to good well completion, proper cementing is one of the most difficult completion phases. Conditions are particularly severe in deviated holes in which casing may be off center. Perforating debris and mud pockets at the cement-formation interface can prevent uniform sand control placement. Completion fluids can cause impairment due to deep bed invasion by entrained solids or dispersion of formation water/sensitive clays, as with mud filtrates. Damage also can occur if the completion fluid is not properly designed and large volumes of bridging materials are lost to the formation.
It is therefore an object of the present invention to provide a new and improved completion system that provides for a well completion using sand control techniques and not requiring killing of the well or snubbing to perform the sand control operation.
In addition, it is an object of this invention to provide a completion system for perforating or opening flow channels into a formation and performing sand control operations in the wellbore, all in one trip into the well.